It is known to produce metal strip by hot-rolling slabs down to a thickness of at most 1 mm. Only a small part of the metal strip produced in this manner can be used directly, that is without subsequent pickling and further treatment such as surface-finishing (known in the art as temper rolling or skin passing) and leveling. The pickling removes roll scale and entails passing the hot strip continuously or discontinuously through an appropriate acid bath.
In a continuous pickling operation lengths of strip are welded together at their ends at the intake of the pickler and cut apart at the downstream end to avoid having to stop the strip in the bath. For the short periods that the strip must be stationary to carry out these joining and separating operations loopers such as described in our commonly owned copending application Ser. No. 169,493 filed July 15, 1981, now U.S. Pat. No. 4,360,137, are provided so that the strip in the bath keeps moving.
In order to thoroughly pickle the hot-rolled strip it is standard to use rolling setups, typically roller-type bend-levelers, immediately before the chemical treatment, that is upstream of the pickling bath. Such mechanical treatment loosens the mill scale so that the pickle can attack it.
Downstream of the pickling bath the clean strip metal is given a rust-preventing coating. Typically grease or thin oil is sprayed over the strip to seal its surface. The strip is then rolled up and the coils are either used as is or further treated, for example leveled, finished, and trimmed, in other locations.
Nowadays it is standard to hot-roll metal strip down very thin, to about 1 mm which is considered the minimum possible thickness. Such strip must be flattened and surface-finished. Bend-leveling is the preferred finishing operation for evening out thickness variations and eliminating anisotropisms in the plane of the workpiece. The resultant product is tough and ductile.
A problem with this style of production is created by the rust-preventing oil film. It makes gripping the strip difficult, and builds up at the rollers. Hence it is necessary to clean the strip, normally by passage through a solvent bath or spray, before such a finishing operation.
Another difficulty in the mass production of hot-rolled metal strip is that it is typically done in a standard rolling string having a width capacity of about 2.2 m. If the initial strip width is reduced to, say, 800 mm, this will underutilize the hot-rolling string laid out for more than twice that width.
It has been suggested to roll a slab about 1650 mm wide and then to split the strip so that the hot-rolling equipment is fully utilized. Unfortunately, since the strip that exits from the hot-rolling string is usually thicker in the center than at the edges, such splitting is fairly difficult and yields strips that are much thicker at one edge than at the other, a shape making downstream guiding of them quite difficult. As a result this procedure has met with no commercial acceptance.